1. Field of the Invention
The present invention relates to a gas sensor. In particular, the present invention relates to a gas sensor which is preferably usable, for example, to measure NOx contained in the atmospheric air and the exhaust gas discharged from vehicles or automobiles.
2. Description of the Related Art
A method of measuring NOx contained in the measurement gas such as the combustion gas is disclosed, for example, in Japanese Laid-Open Patent Publication No. 8-271476. In this method, a first space communicating with the external space and a second space communicating with the first space are provided, and the oxygen concentration is adjusted by using a pumping cell provided in the first space, NOx is reduced or decomposed in the second space, and the NOx concentration is measured from the pumping current flowing through a measuring pumping cell in the second space.
On the other hand, Japanese Laid-Open Patent Publication No. 9-113484 discloses a gas sensor in which an auxiliary pumping cell is provided in a second space so that the oxygen concentration in the second space is controlled to be constant even when the oxygen concentration is suddenly changed.
Further, as a gas sensor disclosed in Japanese Laid-Open Patent Publication No. 11-237362, the measurement accuracy is improved for a detecting electrode by avoiding the influence of pulsation of the exhaust pressure generated in the measurement gas.